The sage lectured brilliantly

The sage lectured brilliantly.
Before him, two images:
"Now this one is a devil,
And this one is me."
He turned away.
Then a cunning pupil
Changed the positions.

Turned the sage again:
"Now this one is a devil,
And this one is me."
The pupils sat, all grinning,
And rejoiced in the game.
But the sage was a sage.